Neoadjuvant Pembrolizumab

Inclusion Criteria: * Histologically or cytologically confirmed NSCLC. * Clinical stage IB (\>/= 3 cm per CT), Stage IIA/IIB, or Stage IIIA (N0-2) amenable to surgical resection. * Primary tumor \>/= 3 cm (for all stages entered) to make it likely that excess tumor will be available after resection. * Patient must be deemed a surgical candidate. * ECOG performance status of 0 or 1 (Appendix C). * No prior chemotherapy, radiation therapy or biologic/targeted therapy for current diagnosis of lung cancer. * Adequate Organ Function * Age ≥18 years. * Non-pregnant. Females of child-bearing potential (not surgically sterilized or postmenopausal \[a woman who is \> 45 years of age and has not had menses for greater than 1 year\]) must test negative for pregnancy within 48 hours prior to any initial study procedure based on a serum pregnancy test. * No active invasive malignancy in the past 2 years other than non-melanoma skin cancer. Cancers that are in-situ are not considered invasive. * Signed written informed consent including HIPAA according to institutional guidelines. * Patients must agree to research blood sampling to participate in study. * Have measurable disease based on RECIST 1.1. * Post-op predicted FEV1 and DLCO \> 40% predicted (or per institutional standard). Exclusion Criteria: * Treatment within the last 30 days with a drug that has not received regulatory approval for any indication at the time of study entry or used an investigational device within 4 weeks of the first dose of treatment. * Has a known history of active TB (Bacillus Tuberculosis). * Hypersensitivity to pembrolizumab or any of its excipients. * Concurrent administration of any other anti-tumor therapy. * Has received prior therapy with an anti-PD-1, anti-PD-L-1, or anti-PD-L2 agent. * Has known active Hepatitis B (e.g., HBsAg reactive) or Hepatitis C (e.g., HCV RNA \[qualitative\] is detected). * Inability to comply with protocol or study procedures. * Active infection requiring antibiotics, antifungal or antiviral agents, that in the opinion of the investigator would compromise the patient's ability to tolerate therapy. * Has known history of, or any evidence of active, non-infectious pneumonitis. * Has a known history of Human Immunodeficiency Virus (HIV) (HIV 1/2 antibodies). * Has active autoimmune disease that has required systemic treatment in the past 2 years (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive drugs). Replacement therapy (e.g. thyroxine, insulin or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency etc) is not considered a form of systemic treatment. Patients with a history of inflammatory bowel disease, including ulcerative colitis and Crohn's Disease, are excluded from this study, as are patients with a history of symptomatic disease (e.g., rheumatoid arthritis, systemic progressive sclerosis \[scleroderma\], systemic lupus erythematosus, autoimmune vasculitis \[eg, Wegener's Granulomatosis\]); motor neuropathy considered of autoimmune origin (e.g. Guillain-Barre Syndrome and Myasthenia Gravis). * Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of trial treatment. * Has a known additional invasive malignancy that is progressing or requires active treatment. Exceptions include basal cell carcinoma of the skin or squamous cell carcinoma of the skin that has undergone potentially curative therapy or in situ cervical cancer. * Is pregnant or breastfeeding, or expecting to conceive or father children within the projected duration of the trial, starting with the pre-screening or screening visit through 120 days after the last dose of trial treatment. * Has had major surgery (other than definitive lung cancer surgery) within two weeks of study or other serious concomitant disorders that in the opinion of the investigator would compromise the safety of the patient or compromise the patient's ability to complete the study. * Has received any non-oncology vaccine therapy used for prevention of infectious diseases (for up to 30 days before or after any dose of pembrolizumab). Note: Seasonal influenza vaccines for injection are generally inactivated flu vaccines and are allowed; however, intranasal influenza vaccines (e.g., Flu-Mist®) are live attenuated vaccines and are not allowed. * Has history of myocardial infarction having occurred less than 6 months before inclusion, any known uncontrolled arrhythmia, symptomatic angina pectoris, active ischemia, or cardiac failure not controlled by medications. Patients with CAD recently treated with surgery and/or stent, if stable without symptomatic angina pectoris, active ischemia are eligible. * Has a history of interstitial lung disease * Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial. * Prisoners or subjects who are compulsorily detained involuntarily incarcerated) for treatment of either psychiatric or physical (e.g., infectious) illness.